US-backed Kurdish militants in northern Syria are heading to the Turkish-assaulted Syrian enclave of Afrin, leading to an "operational pause" in their operations against the Islamic State group, the Pentagon said Monday.

Turkish army officially declared on January 20 the launch of an offensive targeting the positions of People's Protection Units (YPG) in Afrin region in northwest Syria. The Turkish AKP government's excuse was the threat against national interests and border security. The operation has been conducted jointly with the Free Syrian Army (FSA) terrorist group.

Pentagon spokesman Colonel Robert Manning told reporters that the pause meant that some ground operations by the Syrian Democratic Forces (SDF) had been temporarily put on hold. Manning said air strikes by the U.S.-led coalition fighting Islamic State had not been affected and the SDF continue to hold territory taken back from the militant group.

SDF announced on Tuesday they had decided to send their fighters to the Afrin region to help YPG militants fight the Turkish army.

"We are forced to make a decision we did not want to make … We regret this but today we made a painful decision to relocate our fighters from the region east of Euphrates in Deir ez-Zor province … and send them to the Afrin front to repel criminal Turkish aggression," the statement read.

Major Adrian Rankine-Galloway, another Pentagon spokesman, said the U.S. military had seen SDF fighters leave the fight against Islamic State.

"We are aware of the departure of some SDF forces from the Middle Euphrates River Valley," Rakine-Galloway said on Monday. "The Coalition will achieve its goals, but the increased complexity of the situation in Syria can result in operations taking longer."

The United Nations Security Council passed a resolution on Feb. 24 demanding a full month-long ceasefire across Syria excepting only groups that it had designated as terrorists.

The Turkish government has said the ceasefire resolution does not apply to the YPG and has rejected Western calls for it to implement the truce.